Technical Field
The present invention relates to a mask blank, a method of manufacturing a mask blank and a method of manufacturing a transfer mask.
Description of Related Art
The mask blank is used as a base of a transfer mask used in a photolithography method, and the transfer mask is used for a formation of a semiconductor pattern.
As the semiconductor pattern becomes finer, a pattern of the transfer mask used for the formation of the pattern becomes also finer. The transfer mask is manufactured by forming a thin film formed on the mask blank, into a previously set pattern shape.
In the mask blank, it is a resist layer formed on the thin film, that should be pattern-formed first. Therefore, a subject of the present invention is to form a fine pattern with high sensitivity in patterning of the resist layer. As a result, as a resist used when manufacturing the mask blank, a chemically amplified resist with high sensitivity to an exposure light, has been used.
Then, regarding the mask blank and the chemically amplified resist, each document discloses that there are following two points to be improved.
A first point is that when the mask blank is stored or transferred, foreign matters are adhered to an outermost surface of the mask blank.
A second point is that when exposed to an outside air, a contaminant in the outside air is adhered or the chemically amplified resist itself is deteriorated, and the sensitivity cannot be maintained.
In order to improve the above two points, an applicant of the present application discloses a technique of forming a dust-proof protective film made of a water-soluble resin on the chemically amplified resist layer (see patent document 1).